Dongcheng Wang, Yandong Gu, Christopher Stephen, Wenpeng Zhao, Qingfeng Ji
The high-speed coolant pump facilitates thermal regulation in electric vehicle components, including batteries and motors, by circulating an ethylene glycol solution. This commonly used circulating fluid exhibits a notable negative correlation with temperature in terms of viscosity. Numerical simulations investigate the transient dynamics of a high-speed coolant pump operating at 6000 rpm, driving coolant flow at various temperatures. A high-speed coolant pump test rig is established, and the performance is evaluated under different temperature conditions. The numerical simulations at different temperatures align well with the experimental outcomes. Decreasing temperatures, from 100 to −20 °C, lead to reduced pump head and efficiency due to increased viscosity. Specifically, at a flow rate of 30 L/min, head decreases by 40.03% and efficiency by 44.19%. With escalating viscosity, the best efficiency point shifts toward lower flow rates. Notable impacts on both disk efficiency and hydraulic efficiency are observed due to viscosity fluctuations. It exerts minimal influence on volumetric efficiency at elevated flow rates but has a substantial impact on volumetric efficiency at lower flow rates. Increased fluid viscosity causes uneven pressure distribution within the pump, altering velocity profiles within the impeller. High-viscosity fluids tend to form large-scale vortex structures around the blades, reducing the thrust exerted by the blades on the fluid. Higher viscosity results in larger vortex structures around the blades, reducing thrust and increasing fluid frictional resistance. The study findings provide valuable insights for the advancement of high-efficiency, energy-saving, high-speed coolant pumps tailored for electric vehicles.
{"title":"Assessment of viscosity effects on high-speed coolant pump performance","authors":"Dongcheng Wang, Yandong Gu, Christopher Stephen, Wenpeng Zhao, Qingfeng Ji","doi":"10.1063/5.0208753","DOIUrl":"https://doi.org/10.1063/5.0208753","url":null,"abstract":"The high-speed coolant pump facilitates thermal regulation in electric vehicle components, including batteries and motors, by circulating an ethylene glycol solution. This commonly used circulating fluid exhibits a notable negative correlation with temperature in terms of viscosity. Numerical simulations investigate the transient dynamics of a high-speed coolant pump operating at 6000 rpm, driving coolant flow at various temperatures. A high-speed coolant pump test rig is established, and the performance is evaluated under different temperature conditions. The numerical simulations at different temperatures align well with the experimental outcomes. Decreasing temperatures, from 100 to −20 °C, lead to reduced pump head and efficiency due to increased viscosity. Specifically, at a flow rate of 30 L/min, head decreases by 40.03% and efficiency by 44.19%. With escalating viscosity, the best efficiency point shifts toward lower flow rates. Notable impacts on both disk efficiency and hydraulic efficiency are observed due to viscosity fluctuations. It exerts minimal influence on volumetric efficiency at elevated flow rates but has a substantial impact on volumetric efficiency at lower flow rates. Increased fluid viscosity causes uneven pressure distribution within the pump, altering velocity profiles within the impeller. High-viscosity fluids tend to form large-scale vortex structures around the blades, reducing the thrust exerted by the blades on the fluid. Higher viscosity results in larger vortex structures around the blades, reducing thrust and increasing fluid frictional resistance. The study findings provide valuable insights for the advancement of high-efficiency, energy-saving, high-speed coolant pumps tailored for electric vehicles.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"32 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141053666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The hydrodynamic model can be used to describe traffic problems in transport. When the speed of the first car is less than the speed behind it, it leads to traffic jams. When the first car's speed is faster than the cars behind it, it leads to traffic evacuation. If we consider the first car to be a piston, then the speed of the piston will cause traffic jams and traffic evacuation. In this paper, we study the piston problem for the hydrodynamic model. The formation and propagation of shock wave, rarefaction wave, delta-shock wave, and vacuum can describe the phenomena of traffic jams, traffic evacuation, severe traffic jams, and traffic evacuation with traffic volume of zero, respectively. Therefore, for different traffic phenomena, we prove the existence of shock solution, rarefaction solution, delta shock solution, and vacuum solution. In addition, we perform some representative numerical simulations.
{"title":"Piston problem for the pressureless hydrodynamic traffic flow model","authors":"Zhengqi Wang, Lihui Guo, Zhijian Wei","doi":"10.1063/5.0207364","DOIUrl":"https://doi.org/10.1063/5.0207364","url":null,"abstract":"The hydrodynamic model can be used to describe traffic problems in transport. When the speed of the first car is less than the speed behind it, it leads to traffic jams. When the first car's speed is faster than the cars behind it, it leads to traffic evacuation. If we consider the first car to be a piston, then the speed of the piston will cause traffic jams and traffic evacuation. In this paper, we study the piston problem for the hydrodynamic model. The formation and propagation of shock wave, rarefaction wave, delta-shock wave, and vacuum can describe the phenomena of traffic jams, traffic evacuation, severe traffic jams, and traffic evacuation with traffic volume of zero, respectively. Therefore, for different traffic phenomena, we prove the existence of shock solution, rarefaction solution, delta shock solution, and vacuum solution. In addition, we perform some representative numerical simulations.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"197 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141050089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study investigates the production of ferrofluid droplets in a T-junction geometry using the level set method and magnetic force manipulation in the three-dimensional. The analysis reveals key insights into droplet formation processes in four stages: entering, blocking, necking, and detachment. The results show that increasing the Capillary number leads to a significant decrease in volume for non-ferrofluid droplets. Application of a magnetic force enhances the balance of forces during droplet formation, directly impacting droplet volume. Moreover, increasing the magnetic Bond number substantially increases droplet volume, with a more pronounced effect at lower Capillary numbers. Modifying magnetic properties influences droplet volume, with doubling the magnetization results in a significant volume increase. Overall, magnetic forces emerge as a crucial control parameter for droplet volume in ferrofluid systems, offering potential applications in droplet-based technologies and microfluidic devices.
本研究采用水平集方法和三维磁力操纵，研究了铁流体液滴在 T 型接头几何形状中的产生过程。分析揭示了液滴形成过程的四个阶段：进入、阻塞、缩颈和脱离。结果表明，增加毛细管数会导致非ferrofluid液滴体积显著减小。磁力的应用增强了液滴形成过程中的力平衡，直接影响液滴体积。此外，增加磁性邦德数可大幅增加液滴体积，在毛细管数较低时效果更明显。改变磁性会影响液滴体积，磁化率增加一倍会导致体积显著增加。总之，磁力是铁流体系统中液滴体积的关键控制参数，为基于液滴的技术和微流体设备提供了潜在应用。
{"title":"Understanding droplet formation in T-shaped channels with magnetic field influence: A computational investigation","authors":"Masoomeh Darzian Kholardi, M. Farhadi","doi":"10.1063/5.0203322","DOIUrl":"https://doi.org/10.1063/5.0203322","url":null,"abstract":"This study investigates the production of ferrofluid droplets in a T-junction geometry using the level set method and magnetic force manipulation in the three-dimensional. The analysis reveals key insights into droplet formation processes in four stages: entering, blocking, necking, and detachment. The results show that increasing the Capillary number leads to a significant decrease in volume for non-ferrofluid droplets. Application of a magnetic force enhances the balance of forces during droplet formation, directly impacting droplet volume. Moreover, increasing the magnetic Bond number substantially increases droplet volume, with a more pronounced effect at lower Capillary numbers. Modifying magnetic properties influences droplet volume, with doubling the magnetization results in a significant volume increase. Overall, magnetic forces emerge as a crucial control parameter for droplet volume in ferrofluid systems, offering potential applications in droplet-based technologies and microfluidic devices.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"39 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141036945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Constrained by economic development and geographical features, numerous railway lines remain unelectrified, underscoring the expansive potential of diesel trains. Diesel engine emissions discharged from the roof of trains pose a challenge as some of the smoke infiltrates the cabin through the intake of roof-mounted air-conditioning units (ACUs). This intrusion diminishes the indoor air quality, posing health risks to passengers and potentially jeopardizing their safety. This study employs the shear stress transport k-omega turbulence model to formulate a multiphase flow model for simulating smoke diffusion in diesel trains. Additionally, we conducted an optimization design to minimize smoke entry into the ACUs. This study defined six cases based on variations in the shape and height of the cover and the spacing of the smoke vents. The results show that the effect of the diffusion characteristics decreased with the cover height. With the progression of airflow diffusion, the effect of the smoke vent structure on the concentration diminished farther from the vents. The minimum smoke mass flow rate into the intake occurred with the vent spacing of 2.14 m and without a cover, resulting in a 57.0% decrease compared with the maximum. Thus, a smoke vent spacing of 2.14 m without a cover was deemed to be the optimal configuration. The research results provide certain engineering guidance significance for the design and operation of train-smoke vent structures.
{"title":"Numerical study on the effect of smoke emitted from the vents on the roof of a diesel train on the intake of downstream air-conditioning units","authors":"Chunjiang Chen, Qiyue Zhang, Zhuojun Li, Yamin Ma, Liangzhong Xu, Weisi Gong, Jiqiang Niu","doi":"10.1063/5.0202799","DOIUrl":"https://doi.org/10.1063/5.0202799","url":null,"abstract":"Constrained by economic development and geographical features, numerous railway lines remain unelectrified, underscoring the expansive potential of diesel trains. Diesel engine emissions discharged from the roof of trains pose a challenge as some of the smoke infiltrates the cabin through the intake of roof-mounted air-conditioning units (ACUs). This intrusion diminishes the indoor air quality, posing health risks to passengers and potentially jeopardizing their safety. This study employs the shear stress transport k-omega turbulence model to formulate a multiphase flow model for simulating smoke diffusion in diesel trains. Additionally, we conducted an optimization design to minimize smoke entry into the ACUs. This study defined six cases based on variations in the shape and height of the cover and the spacing of the smoke vents. The results show that the effect of the diffusion characteristics decreased with the cover height. With the progression of airflow diffusion, the effect of the smoke vent structure on the concentration diminished farther from the vents. The minimum smoke mass flow rate into the intake occurred with the vent spacing of 2.14 m and without a cover, resulting in a 57.0% decrease compared with the maximum. Thus, a smoke vent spacing of 2.14 m without a cover was deemed to be the optimal configuration. The research results provide certain engineering guidance significance for the design and operation of train-smoke vent structures.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"28 20","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141054226","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Field inversion machine learning (FIML) has the advantages of model consistency and low data dependency and has been used to augment imperfect turbulence models. However, the solver-intrusive field inversion has a high entry bar, and existing FIML studies focused on improving only steady-state or time-averaged periodic flow predictions. To break this limit, this paper develops an open-source FIML framework for time-accurate unsteady flow, where both spatial and temporal variations of flow are of interest. We augment a Reynolds-Averaged Navier–Stokes (RANS) turbulence model's production term with a scalar field. We then integrate a neural network (NN) model into the flow solver to compute the above augmentation scalar field based on local flow features at each time step. Finally, we optimize the weights and biases of the built-in NN model to minimize the regulated spatial-temporal prediction error between the augmented flow solver and reference data. We consider the spatial-temporal evolution of unsteady flow over a 45° ramp and use only the surface pressure as the training data. The unsteady-FIML-trained model accurately predicts the spatial-temporal variations of unsteady flow fields. In addition, the trained model exhibits reasonably good prediction accuracy for various ramp angles, Reynolds numbers, and flow variables (e.g., velocity fields) that are not used in training, highlighting its generalizability. The FIML capability has been integrated into our open-source framework DAFoam. It has the potential to train more accurate RANS turbulence models for other unsteady flow phenomena, such as wind gust response, bubbly flow, and particle dispersion in the atmosphere.
{"title":"Field inversion machine learning augmented turbulence modeling for time-accurate unsteady flow","authors":"Lean Fang, Ping He","doi":"10.1063/5.0207704","DOIUrl":"https://doi.org/10.1063/5.0207704","url":null,"abstract":"Field inversion machine learning (FIML) has the advantages of model consistency and low data dependency and has been used to augment imperfect turbulence models. However, the solver-intrusive field inversion has a high entry bar, and existing FIML studies focused on improving only steady-state or time-averaged periodic flow predictions. To break this limit, this paper develops an open-source FIML framework for time-accurate unsteady flow, where both spatial and temporal variations of flow are of interest. We augment a Reynolds-Averaged Navier–Stokes (RANS) turbulence model's production term with a scalar field. We then integrate a neural network (NN) model into the flow solver to compute the above augmentation scalar field based on local flow features at each time step. Finally, we optimize the weights and biases of the built-in NN model to minimize the regulated spatial-temporal prediction error between the augmented flow solver and reference data. We consider the spatial-temporal evolution of unsteady flow over a 45° ramp and use only the surface pressure as the training data. The unsteady-FIML-trained model accurately predicts the spatial-temporal variations of unsteady flow fields. In addition, the trained model exhibits reasonably good prediction accuracy for various ramp angles, Reynolds numbers, and flow variables (e.g., velocity fields) that are not used in training, highlighting its generalizability. The FIML capability has been integrated into our open-source framework DAFoam. It has the potential to train more accurate RANS turbulence models for other unsteady flow phenomena, such as wind gust response, bubbly flow, and particle dispersion in the atmosphere.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"90 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141032359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Gas dispersion in non-Newtonian fluids has numerous applications in many chemical and biochemical applications. However, the effect of the power-law model constants describing the rheological behavior of the pseudoplastic fluid has never been investigated. Thus, a numerical model was developed to simulate the hydrodynamics of gas dispersion in non-Newtonian fluids with a coaxial mixer. Then, a set of experiments was conducted to assess the mass transfer efficacy of a coaxial mixer to benchmark the numerical model. In this regard, various methods, including dynamic gassing-in and electrical resistance tomography methods, were used to quantify the mass transfer and gas hold-up profiles. The influence of fluid rheological properties, gas flow number, and rotating mode on the power consumption, mass transfer coefficient, bubble size profile, and hydrodynamics were examined both experimentally and numerically. The response surface model (RSM) was employed to explore the individual effects of power-law model constants on mass transfer. The RSM model utilized five levels for the consistency index (k), five levels for the flow index (n), and three levels for the gas flow number. The statistical model proposed that the absolute model constants for the flow and consistency indices were 0.0012 and 0.0010, respectively, for the co-rotating mixer. Conversely, for the counter-rotating mixer, these constants were 0.0010 and 0.0013, respectively. Therefore, this study revealed that the co-rotating coaxial mixer was well-suited for dispersing gas within a fluid with high consistency. In contrast, the counter-rotating mixer proved effective in enhancing gas dispersion within a fluid with a lower flow index.
{"title":"Influence of rheological parameters on the performance of the aerated coaxial mixer containing a pseudoplastic fluid","authors":"A. Rahimzadeh, F. Ein‐Mozaffari, A. Lohi","doi":"10.1063/5.0202461","DOIUrl":"https://doi.org/10.1063/5.0202461","url":null,"abstract":"Gas dispersion in non-Newtonian fluids has numerous applications in many chemical and biochemical applications. However, the effect of the power-law model constants describing the rheological behavior of the pseudoplastic fluid has never been investigated. Thus, a numerical model was developed to simulate the hydrodynamics of gas dispersion in non-Newtonian fluids with a coaxial mixer. Then, a set of experiments was conducted to assess the mass transfer efficacy of a coaxial mixer to benchmark the numerical model. In this regard, various methods, including dynamic gassing-in and electrical resistance tomography methods, were used to quantify the mass transfer and gas hold-up profiles. The influence of fluid rheological properties, gas flow number, and rotating mode on the power consumption, mass transfer coefficient, bubble size profile, and hydrodynamics were examined both experimentally and numerically. The response surface model (RSM) was employed to explore the individual effects of power-law model constants on mass transfer. The RSM model utilized five levels for the consistency index (k), five levels for the flow index (n), and three levels for the gas flow number. The statistical model proposed that the absolute model constants for the flow and consistency indices were 0.0012 and 0.0010, respectively, for the co-rotating mixer. Conversely, for the counter-rotating mixer, these constants were 0.0010 and 0.0013, respectively. Therefore, this study revealed that the co-rotating coaxial mixer was well-suited for dispersing gas within a fluid with high consistency. In contrast, the counter-rotating mixer proved effective in enhancing gas dispersion within a fluid with a lower flow index.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"102 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141037593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, we present a mathematical model aimed at describing both the effusive and relaxing phase of pancakelike lava domes on the Venus surface. Our model moves from the recent paper by Quick et al. [“New approaches to inferences for steep-sided domes on Venus,” J. Volcanol. Geotherm. Res. 319, 93–105 (2016)] but generalizes it under several respects. Indeed, we consider a temperature field, playing a fundamental role in the flow evolution, whose dynamics is governed by the heat equation. In particular, we suggest that the main mechanism that drives cooling is radiation at the dome surface. We obtain a generalized form of the equation describing the dome shape, where the dependence of viscosity on temperature is taken into account. Still following Quick et al. [“New approaches to inferences for steep-sided domes on Venus,” J. Volcanol. Geothermal Res. 319, 93–105 (2016)], we distinguish an isothermal relaxing phase preceded by a non-isothermal (cooling) effusive phase, but the fluid mechanical model, developed in an axisymmetric thin-layer approximation, takes into account both shear thinning and thermal effects. In both cases (relaxing and effusive phase), we show the existence of self-similar solutions. In particular, this allows to obtain a likely scenario of the volumetric flow rate which originated this kind of domes. Indeed, the model predicts a time varying discharge, which is maximum at the beginning of the formation process and decreases until vanishing when the effusive phase is over. The model, in addition to fitting well the dome shape, suggests a possible forming scenario, which may help the largely debated questions about the emplacement and lava composition of these domes.
{"title":"Thermo-mechanical modeling of pancakelike domes on Venus","authors":"Benedetta Calusi, A. Farina, L. Fusi, Fabio Rosso","doi":"10.1063/5.0209674","DOIUrl":"https://doi.org/10.1063/5.0209674","url":null,"abstract":"In this paper, we present a mathematical model aimed at describing both the effusive and relaxing phase of pancakelike lava domes on the Venus surface. Our model moves from the recent paper by Quick et al. [“New approaches to inferences for steep-sided domes on Venus,” J. Volcanol. Geotherm. Res. 319, 93–105 (2016)] but generalizes it under several respects. Indeed, we consider a temperature field, playing a fundamental role in the flow evolution, whose dynamics is governed by the heat equation. In particular, we suggest that the main mechanism that drives cooling is radiation at the dome surface. We obtain a generalized form of the equation describing the dome shape, where the dependence of viscosity on temperature is taken into account. Still following Quick et al. [“New approaches to inferences for steep-sided domes on Venus,” J. Volcanol. Geothermal Res. 319, 93–105 (2016)], we distinguish an isothermal relaxing phase preceded by a non-isothermal (cooling) effusive phase, but the fluid mechanical model, developed in an axisymmetric thin-layer approximation, takes into account both shear thinning and thermal effects. In both cases (relaxing and effusive phase), we show the existence of self-similar solutions. In particular, this allows to obtain a likely scenario of the volumetric flow rate which originated this kind of domes. Indeed, the model predicts a time varying discharge, which is maximum at the beginning of the formation process and decreases until vanishing when the effusive phase is over. The model, in addition to fitting well the dome shape, suggests a possible forming scenario, which may help the largely debated questions about the emplacement and lava composition of these domes.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"2009 20","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141027108","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mahdiyar Khanpour, A. Mohammadian, H. Shirkhani, Reza Kianoush
This research focuses on employing a linear analytical approach to transform free surface waves and velocities into mode coordinates, with the aim of investigating the free vibration behavior of a coupled system consisting of a Single Degree of Freedom and a sloshing tank. Through a series of manipulations and simplifications of the coupled equations, a fourth-order ordinary differential equation is derived to showcase the overall response of the system, highlighting the contribution of each odd mode. Key concepts explored include system stability, mode-specific natural periods, establishment of initial boundary conditions, and formulation of the complete system response. The analytical method applied to study Tuned Liquid Dampers, a type of elevated sloshing tank, reveals that in higher modes, the lower frequency aligns with the structural natural frequency, while the higher frequency is approximately n times the structural natural frequency (where n is the odd mode number). This approach also elucidates why the system's response does not exhibit a higher-frequency component in higher modes. The study further investigates concepts such as employing an initial perturbation to excite higher frequencies and the potential for approximating the system through the first mode. Additionally, a numerical model was developed using variable separation and modal decomposition methods to complement and validate the analytical approach. Finally, further verification of the model was performed using the Preismann scheme applied to the relevant equations and the central upwind applied to nonlinear equations.
本研究的重点是采用线性分析方法将自由表面波和速度转换为模态坐标，目的是研究由单自由度和滑动槽组成的耦合系统的自由振动行为。通过对耦合方程的一系列处理和简化，得出了一个四阶常微分方程，以展示系统的整体响应，突出每个奇数模式的贡献。探讨的关键概念包括系统稳定性、特定模式的自然周期、初始边界条件的建立以及完整系统响应的表述。在研究调谐液体阻尼器（一种高架荡槽）时采用的分析方法显示，在较高的模式中，较低的频率与结构固有频率一致，而较高的频率大约是结构固有频率的 n 倍（其中 n 为奇数模式数）。这种方法还解释了为什么在较高模态下系统响应没有表现出较高频率成分。研究还进一步探究了一些概念，如采用初始扰动来激发更高频率，以及通过第一模态近似系统的可能性。此外，还利用变量分离和模态分解方法开发了一个数值模型，以补充和验证分析方法。最后，利用应用于相关方程的 Preismann 方案和应用于非线性方程的中央上风法对该模型进行了进一步验证。
{"title":"Analytical solution to a coupled system including tuned liquid damper and single degree of freedom under free vibration with modal decomposition method","authors":"Mahdiyar Khanpour, A. Mohammadian, H. Shirkhani, Reza Kianoush","doi":"10.1063/5.0206390","DOIUrl":"https://doi.org/10.1063/5.0206390","url":null,"abstract":"This research focuses on employing a linear analytical approach to transform free surface waves and velocities into mode coordinates, with the aim of investigating the free vibration behavior of a coupled system consisting of a Single Degree of Freedom and a sloshing tank. Through a series of manipulations and simplifications of the coupled equations, a fourth-order ordinary differential equation is derived to showcase the overall response of the system, highlighting the contribution of each odd mode. Key concepts explored include system stability, mode-specific natural periods, establishment of initial boundary conditions, and formulation of the complete system response. The analytical method applied to study Tuned Liquid Dampers, a type of elevated sloshing tank, reveals that in higher modes, the lower frequency aligns with the structural natural frequency, while the higher frequency is approximately n times the structural natural frequency (where n is the odd mode number). This approach also elucidates why the system's response does not exhibit a higher-frequency component in higher modes. The study further investigates concepts such as employing an initial perturbation to excite higher frequencies and the potential for approximating the system through the first mode. Additionally, a numerical model was developed using variable separation and modal decomposition methods to complement and validate the analytical approach. Finally, further verification of the model was performed using the Preismann scheme applied to the relevant equations and the central upwind applied to nonlinear equations.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"6 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141036194","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pratik Mahyawansi, Sumit R. Zanje, Abbas Sharifi, Dwayne McDaniel, Arturo S. Leon
The storm sewer geyser is a process where an air–water mixture violently erupts from a manhole. Despite the low hydrostatic pressure, violent eruptions can achieve a height of tens of meters above the ground. This current study experimentally investigates large-scale violent geysers using a large air pocket inserted from a pressurized air tank. The total length of the pipe system is approximately 88 m with a 0.1572 m diameter pipe. This large-scale experiment facilitates the investigation of spontaneous geyser eruptions. This study identifies the role of air–water volume ratio and coefficient of pressure (ratio of absolute initial static pressure to initial dynamic pressure) on the geyser intensity using eruption images and pressure plots. A total of 116 cases are tested, in which the volume ratio is parametrically increased from 0 to 1.1 under various operating conditions. A geyser score is defined to quantify the geyser eruption nature based on visual observations. The key findings are as follows: first, a sharp transition in geyser intensity is observed at the critical volume ratio of 0.5, and pre-transition and post-transition intensity exhibit a linear relationship with the volume ratio; and second, the critical volume ratio linearly varies with the coefficient of pressure.
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Boiling of the coolant at the hot surface provides relatively better cooling by absorbing latent heat along with convection heat transfer as compared to heat transfer under single-phase conditions. In boiling, the orientation of heated surface also plays a crucial role. Downward facing boiling is complex than upward facing boiling, as the detachment of the bubble inhibited due to the heater surface orientation. Consequently, the bubble residence time and interaction with other bubbles are different in such boiling conditions. Our experiments on a large downward facing flat surface (100 × 400 mm2) revealed unexplored boiling phenomena. The boiling process is dominated by a complex engulfing phenomenon, which is rarely reported in the past. The engulfing phenomena have been captured using high-speed photography, wherein, at low heat fluxes, it is observed that larger bubbles engulf small bubbles by opening their mouth and swallowing the small bubbles. However, at higher heat fluxes, this phenomenon disappears. A larger vapor blanket is formed due to engulfing of bubbles, which may lead to departure from nucleate boiling. This engulfing behavior depends on the heat flux and subcooling. With the increase in heat flux, it is found that the rate of vapor engulfing increases. We have attempted to explain the science behind such engulfing phenomenon based on the capillary pressure difference. These results are consistent at various subcooling. This research provides new insights into nucleate boiling and may help in developing advanced mathematical models for accurate heat transfer prediction on downward facing nucleate boiling.
{"title":"Engulfing behavior of vapor bubbles in downward facing heated surface boiling","authors":"P. K. Verma, Arun Kumar Nayak","doi":"10.1063/5.0203621","DOIUrl":"https://doi.org/10.1063/5.0203621","url":null,"abstract":"Boiling of the coolant at the hot surface provides relatively better cooling by absorbing latent heat along with convection heat transfer as compared to heat transfer under single-phase conditions. In boiling, the orientation of heated surface also plays a crucial role. Downward facing boiling is complex than upward facing boiling, as the detachment of the bubble inhibited due to the heater surface orientation. Consequently, the bubble residence time and interaction with other bubbles are different in such boiling conditions. Our experiments on a large downward facing flat surface (100 × 400 mm2) revealed unexplored boiling phenomena. The boiling process is dominated by a complex engulfing phenomenon, which is rarely reported in the past. The engulfing phenomena have been captured using high-speed photography, wherein, at low heat fluxes, it is observed that larger bubbles engulf small bubbles by opening their mouth and swallowing the small bubbles. However, at higher heat fluxes, this phenomenon disappears. A larger vapor blanket is formed due to engulfing of bubbles, which may lead to departure from nucleate boiling. This engulfing behavior depends on the heat flux and subcooling. With the increase in heat flux, it is found that the rate of vapor engulfing increases. We have attempted to explain the science behind such engulfing phenomenon based on the capillary pressure difference. These results are consistent at various subcooling. This research provides new insights into nucleate boiling and may help in developing advanced mathematical models for accurate heat transfer prediction on downward facing nucleate boiling.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"2014 27","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141027093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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